"Gregory Craig's involvement in this case is disturbing," said the watchdog, Joe Sinsheimer. "It raises the question of whether political influence can be bought and sold in Washington, D.C., even in criminal inquiries."

Craig is a high-profile Washington power broker who served as White House counsel during the first year of the Obama administration. He left the post late in 2009 and returned to private practice.

Craig did not immediately respond Friday to a request for comment from ABC News, but in an interview Thursday with a North Carolina newspaper he said he has been in discussions with critical "decision makers" at the Department of Justice, advocating on behalf of Edwards.

Craig's recent role at the White House and his connections in the Justice Department are troubling to Sinsheimer.

"Mr. Craig is using the relationships he formed as White House legal counsel to try to manipulate a criminal investigation," he argued. "While Mr. Craig's actions may be technically legal, they violate the spirit of the law, which requires a two-year cooling off period before government officials can seek to influence their old colleagues."

In an interview with National Public Radio, which first reported Craig's hiring, Craig said those "revolving-door" rules apply to only the top three tiers of Justice Department officials. The Edwards' case is being led by the DOJ's Public Integrity Section, and Craig argued that the prohibitions do not apply to the lawyers and assistants there.

"I'm sure there's nothing illegal in what he's doing," said Trevor Potter, president of the non-partisan Campaign Legal Center. "But it's pretty close. If he's been hired to deal with the Obama administration, then they've clearly hired a well-connected person."

John Edwards Federal Grand Jury Could Decide Soon

For more than two years, a federal grand jury has been hearing evidence in connection with more than $1 million that allegedly was used to support Edwards' mistress, Rielle Hunter, and to hide his affair with her.

At its core, the investigation seeks to connect Edwards to those payments and, further, to show that he knew the payments were made with the intention of keeping his presidential campaign viable.

Sources with knowledge of the case have told ABC News that the investigation is complete and a final resolution could come before the end of March.

Craig has a reputation as a savvy negotiator accustomed to taking on high-profile clients. He is perhaps best known for his defense of former President Clinton during impeachment proceedings, but he also has represented the late Sen. Ted Kennedy and John Hinckley, Jr., who was found not guilty by reason of insanity after an assassination attempt on President Reagan.

Once his involvement became known, Craig quickly offered a blunt assessment of the case in an interview with the Raleigh News and Observer.

"There is no violation of law here," he told the paper.

To bring criminal charges against Edwards for payments to his mistress, he said, "would be an unprecedented application of the campaign-finance laws. It's a huge stretch."

Those comments prompted a strong reaction from Sinsheimer, the North Carolina political watchdog.

"Nothing could be farther from truth," he told ABC News. "Federal law may not have anticipated a presidential candidate using over a half million dollars of political donors' money to hide his mistress from public view during a campaign, but that doesn't mean federal prosecutors shouldn't investigate."

Officials at the U.S. Attorney's office in Raleigh did not return calls Friday seeking comment.